An optical fiber connector includes a ferrule, which is a cylindrical ceramic element, having a centrally mounted optical fiber. An optical fiber connector also includes a connector housing which is physically mounted to a fiber optic cable and the ferrule. Optical fibers and ferrules in fiber optic connectors require a high quality, optical grade endface surface to maximize coupling efficiency and ensure proper operation. Generally a fiber endface has a desirable geometry or topography, such as a desirable radius of curvature, apex offset and fiber height. The fiber endface also has an acceptable surface quality free of any undesirable surface defects.
The proper surface quality and topography of a fiber endface in a fiber connector is achieved through an optical polishing process. During this process a plurality of fiber optic connectors or fiber optic connector ferrules are mounted in a polishing plate or work holder. The work holder determines the position and polish angle of the ferrules during the polishing process. The connectors are mounted in a way such that the endface of the ferrule protrudes slightly past the bottom surface of the polishing plate. The polishing plate is repetitively moved over an abrasive surface, or pad, in a systematic manner. The abrasive pad removes material from the protruding portion or endface of the ferrule. The desired ferrule endface geometry and surface quality is achieved by changing the polishing variables such as the type of abrasive material used, pressure and speed applied and the time of polishing.
There are a large number of factors that influence the end result of the polishing process. Examples of these factors are tool wear, temperature variations, material variations, external physical contaminants and skill of the operator. Depending on the level of control exercised over these variables, the result of the polishing process can vary significantly between iterations. Therefore, to ensure desired polishing results, it is necessary to inspect the endface quality and test the topography of the fiber connector during and after the polishing process.
The surface quality of the fiber endface can be evaluated using an optical microscope to magnify any surface defects that might be present on the fiber endface surface. The fiber endface geometry can be measured using several different contact, or non-contact, three-dimensional surface mapping methods. For example, optical interferometry is a very practical and accurate measurement technique and is commonly used for inspecting endfaces.
In general, testing and inspecting the connector endfaces using conventional means requires that each ferrule, or connector, be physically removed from the work holder and placed into a separate testing instrument for evaluation. If the ferrule endface does not have the required parameters it must be re-inserted back into the polishing plate for further processing or considered rejected. It may be necessary to repeat this testing procedure several times with each ferrule during the fabrication process.
Such testing procedures require excessive material handling of the sensitive ferrules and can be very time consuming. Furthermore, the removal and subsequent re-insertion of the ferrule from the polishing plate may introduce minute positional changes and other variables that further impede the predictability of the polishing process. It is generally undesirable to remove the ferrule from the polishing tool until the polishing process is complete.